2 FreeRTOS V7.5.2 - Copyright (C) 2013 Real Time Engineers Ltd.
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4 VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
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6 ***************************************************************************
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8 * FreeRTOS provides completely free yet professionally developed, *
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9 * robust, strictly quality controlled, supported, and cross *
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10 * platform software that has become a de facto standard. *
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12 * Help yourself get started quickly and support the FreeRTOS *
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13 * project by purchasing a FreeRTOS tutorial book, reference *
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14 * manual, or both from: http://www.FreeRTOS.org/Documentation *
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18 ***************************************************************************
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20 This file is part of the FreeRTOS distribution.
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22 FreeRTOS is free software; you can redistribute it and/or modify it under
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23 the terms of the GNU General Public License (version 2) as published by the
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24 Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.
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26 >>! NOTE: The modification to the GPL is included to allow you to distribute
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27 >>! a combined work that includes FreeRTOS without being obliged to provide
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28 >>! the source code for proprietary components outside of the FreeRTOS
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31 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
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32 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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33 FOR A PARTICULAR PURPOSE. Full license text is available from the following
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34 link: http://www.freertos.org/a00114.html
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38 ***************************************************************************
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40 * Having a problem? Start by reading the FAQ "My application does *
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41 * not run, what could be wrong?" *
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43 * http://www.FreeRTOS.org/FAQHelp.html *
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45 ***************************************************************************
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47 http://www.FreeRTOS.org - Documentation, books, training, latest versions,
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48 license and Real Time Engineers Ltd. contact details.
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50 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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51 including FreeRTOS+Trace - an indispensable productivity tool, a DOS
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52 compatible FAT file system, and our tiny thread aware UDP/IP stack.
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54 http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
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55 Integrity Systems to sell under the OpenRTOS brand. Low cost OpenRTOS
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56 licenses offer ticketed support, indemnification and middleware.
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58 http://www.SafeRTOS.com - High Integrity Systems also provide a safety
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59 engineered and independently SIL3 certified version for use in safety and
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60 mission critical applications that require provable dependability.
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66 The tasks defined on this page demonstrate the use of recursive mutexes.
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68 For recursive mutex functionality the created mutex should be created using
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69 xSemaphoreCreateRecursiveMutex(), then be manipulated
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70 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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73 This demo creates three tasks all of which access the same recursive mutex:
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75 prvRecursiveMutexControllingTask() has the highest priority so executes
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76 first and grabs the mutex. It then performs some recursive accesses -
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77 between each of which it sleeps for a short period to let the lower
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78 priority tasks execute. When it has completed its demo functionality
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79 it gives the mutex back before suspending itself.
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81 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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82 a blocking 'take'. The blocking task has a lower priority than the
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83 controlling task so by the time it executes the mutex has already been
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84 taken by the controlling task, causing the blocking task to block. It
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85 does not unblock until the controlling task has given the mutex back,
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86 and it does not actually run until the controlling task has suspended
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87 itself (due to the relative priorities). When it eventually does obtain
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88 the mutex all it does is give the mutex back prior to also suspending
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89 itself. At this point both the controlling task and the blocking task are
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92 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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93 a tight loop attempting to obtain the mutex with a non-blocking call. As
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94 the lowest priority task it will not successfully obtain the mutex until
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95 both the controlling and blocking tasks are suspended. Once it eventually
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96 does obtain the mutex it first unsuspends both the controlling task and
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97 blocking task prior to giving the mutex back - resulting in the polling
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98 task temporarily inheriting the controlling tasks priority.
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101 /* Scheduler include files. */
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102 #include "FreeRTOS.h"
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104 #include "semphr.h"
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106 /* Demo app include files. */
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107 #include "recmutex.h"
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109 /* Priorities assigned to the three tasks. */
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110 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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111 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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112 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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114 /* In this version the tick period is very long, so the short delay cannot be
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115 for too many ticks, or the check task will execute and find that the recmutex
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116 tasks have not completed their functionality and then signal an error. The
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117 delay does however have to be long enough to allow the lower priority tasks
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118 a chance of executing - this is basically achieved by reducing the number
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119 of times the loop that takes/gives the recursive mutex executes. */
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120 #define recmuMAX_COUNT ( 2 )
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121 #define recmuSHORT_DELAY ( 20 )
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122 #define recmuNO_DELAY ( ( portTickType ) 0 )
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123 #define recmuFIVE_TICK_DELAY ( ( portTickType ) 5 )
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125 /* The three tasks as described at the top of this file. */
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126 static void prvRecursiveMutexControllingTask( void *pvParameters );
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127 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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128 static void prvRecursiveMutexPollingTask( void *pvParameters );
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130 /* The mutex used by the demo. */
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131 static xSemaphoreHandle xMutex;
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133 /* Variables used to detect and latch errors. */
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134 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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135 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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137 /* Handles of the two higher priority tasks, required so they can be resumed
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139 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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141 /*-----------------------------------------------------------*/
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143 void vStartRecursiveMutexTasks( void )
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145 /* Just creates the mutex and the three tasks. */
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147 xMutex = xSemaphoreCreateRecursiveMutex();
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149 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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150 in use. The registry is provided as a means for kernel aware
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151 debuggers to locate mutex and has no purpose if a kernel aware debugger
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152 is not being used. The call to vQueueAddToRegistry() will be removed
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153 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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154 defined to be less than 1. */
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155 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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158 if( xMutex != NULL )
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160 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1Ctrl", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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161 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2Blck", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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162 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3Poll", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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165 /*-----------------------------------------------------------*/
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167 static void prvRecursiveMutexControllingTask( void *pvParameters )
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169 unsigned portBASE_TYPE ux;
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171 /* Just to remove compiler warning. */
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172 ( void ) pvParameters;
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176 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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177 it. The first time through, the mutex will not have been used yet,
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178 subsequent times through, at this point the mutex will be held by the
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180 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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182 xErrorOccurred = pdTRUE;
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185 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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187 /* We should now be able to take the mutex as many times as
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190 The first time through the mutex will be immediately available, on
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191 subsequent times through the mutex will be held by the polling task
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192 at this point and this Take will cause the polling task to inherit
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193 the priority of this task. In this case the block time must be
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194 long enough to ensure the polling task will execute again before the
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195 block time expires. If the block time does expire then the error
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196 flag will be set here. */
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197 if( xSemaphoreTakeRecursive( xMutex, recmuFIVE_TICK_DELAY ) != pdPASS )
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199 xErrorOccurred = pdTRUE;
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202 /* Ensure the other task attempting to access the mutex (and the
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203 other demo tasks) are able to execute to ensure they either block
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204 (where a block time is specified) or return an error (where no
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205 block time is specified) as the mutex is held by this task. */
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206 vTaskDelay( recmuSHORT_DELAY );
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209 /* For each time we took the mutex, give it back. */
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210 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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212 /* Ensure the other task attempting to access the mutex (and the
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213 other demo tasks) are able to execute. */
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214 vTaskDelay( recmuSHORT_DELAY );
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216 /* We should now be able to give the mutex as many times as we
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217 took it. When the mutex is available again the Blocking task
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218 should be unblocked but not run because it has a lower priority
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219 than this task. The polling task should also not run at this point
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220 as it too has a lower priority than this task. */
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221 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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223 xErrorOccurred = pdTRUE;
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227 /* Having given it back the same number of times as it was taken, we
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228 should no longer be the mutex owner, so the next give should fail. */
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229 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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231 xErrorOccurred = pdTRUE;
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234 /* Keep count of the number of cycles this task has performed so a
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235 stall can be detected. */
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236 uxControllingCycles++;
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238 /* Suspend ourselves so the blocking task can execute. */
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239 xControllingIsSuspended = pdTRUE;
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240 vTaskSuspend( NULL );
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241 xControllingIsSuspended = pdFALSE;
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244 /*-----------------------------------------------------------*/
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246 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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248 /* Just to remove compiler warning. */
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249 ( void ) pvParameters;
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253 /* This task will run while the controlling task is blocked, and the
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254 controlling task will block only once it has the mutex - therefore
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255 this call should block until the controlling task has given up the
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256 mutex, and not actually execute past this call until the controlling
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257 task is suspended. */
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258 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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260 if( xControllingIsSuspended != pdTRUE )
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262 /* Did not expect to execute until the controlling task was
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264 xErrorOccurred = pdTRUE;
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268 /* Give the mutex back before suspending ourselves to allow
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269 the polling task to obtain the mutex. */
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270 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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272 xErrorOccurred = pdTRUE;
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275 xBlockingIsSuspended = pdTRUE;
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276 vTaskSuspend( NULL );
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277 xBlockingIsSuspended = pdFALSE;
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282 /* We should not leave the xSemaphoreTakeRecursive() function
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283 until the mutex was obtained. */
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284 xErrorOccurred = pdTRUE;
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287 /* The controlling and blocking tasks should be in lock step. */
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288 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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290 xErrorOccurred = pdTRUE;
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293 /* Keep count of the number of cycles this task has performed so a
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294 stall can be detected. */
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295 uxBlockingCycles++;
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298 /*-----------------------------------------------------------*/
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300 static void prvRecursiveMutexPollingTask( void *pvParameters )
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302 /* Just to remove compiler warning. */
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303 ( void ) pvParameters;
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307 /* Keep attempting to obtain the mutex. We should only obtain it when
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308 the blocking task has suspended itself, which in turn should only
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309 happen when the controlling task is also suspended. */
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310 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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312 /* Is the blocking task suspended? */
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313 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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315 xErrorOccurred = pdTRUE;
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319 /* Keep count of the number of cycles this task has performed
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320 so a stall can be detected. */
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323 /* We can resume the other tasks here even though they have a
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324 higher priority than the polling task. When they execute they
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325 will attempt to obtain the mutex but fail because the polling
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326 task is still the mutex holder. The polling task (this task)
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327 will then inherit the higher priority. The Blocking task will
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328 block indefinitely when it attempts to obtain the mutex, the
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329 Controlling task will only block for a fixed period and an
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330 error will be latched if the polling task has not returned the
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331 mutex by the time this fixed period has expired. */
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332 vTaskResume( xBlockingTaskHandle );
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333 vTaskResume( xControllingTaskHandle );
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335 /* The other two tasks should now have executed and no longer
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337 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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339 xErrorOccurred = pdTRUE;
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342 /* Release the mutex, disinheriting the higher priority again. */
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343 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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345 xErrorOccurred = pdTRUE;
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350 #if configUSE_PREEMPTION == 0
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357 /*-----------------------------------------------------------*/
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359 /* This is called to check that all the created tasks are still running. */
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360 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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362 portBASE_TYPE xReturn;
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363 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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365 /* Is the controlling task still cycling? */
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366 if( uxLastControllingCycles == uxControllingCycles )
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368 xErrorOccurred = pdTRUE;
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372 uxLastControllingCycles = uxControllingCycles;
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375 /* Is the blocking task still cycling? */
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376 if( uxLastBlockingCycles == uxBlockingCycles )
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378 xErrorOccurred = pdTRUE;
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382 uxLastBlockingCycles = uxBlockingCycles;
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385 /* Is the polling task still cycling? */
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386 if( uxLastPollingCycles == uxPollingCycles )
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388 xErrorOccurred = pdTRUE;
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392 uxLastPollingCycles = uxPollingCycles;
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395 if( xErrorOccurred == pdTRUE )
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